The present invention relates to aircraft, and more particularly to an aircraft with vertical take-off and landing (VTOL) capabilities and high speed (HS) horizontal flight.
As is well known, conventional high speed winged aircraft require long runways for take-offs and landings. There are many significant disadvantages to the long runways required for take-off and landing. One such disadvantage is the vulnerability of air bases in combat zones. By simply destroying a portion of the runway, an enemy can effectively shut down an air base. This could have catastrophic effects since it removes the ability to attack from this location, often prevents those at the air base from leaving and stops incoming supplies.
Another significant military disadvantage is that conventional runways are costly and require considerable time to construct and, thus, most air bases are constructed a considerable distance from the battlefront. For this reason, considerable time and expense is required merely to fly the aircraft to the combat area.
With the need for a runway for take-off and landing, conventional aircraft must line up and wait to take off or land thus resulting in significant wastes of time in both military and domestic air travel.
Conventional aircraft are also susceptible to delays in inclement weather conditions as a direct result of the runway requirement. Traffic control is much more difficult, and snow and ice can even cause extended shut-downs of the runways.
With regard to domestic air travel, the noise created by and clearance required by ascending and descending aircraft has forced airports to be built considerable distances from the metropolitan areas that they serve. The large areas of land required for constructing the long take-off and landing runways have also forced airports to be constructed away from the metropolitan areas. In many cases, the metropolitan area has expanded to encompass the airport thus restricting growth of the airport as well as creating serious safety and health concerns.
Of course, the conventional helicopter, with its vertical takeoff and landing capabilities, overcomes these problems, but is not without its own shortcomings. Presently, helicopters are significantly restricted in their range capabilities. Helicopters also suffer generally severe payload restrictions compared to winged aircraft; and furthermore, fly at substantially less horizontal speeds than winged aircraft due to the greater aerodynamic drag created by their design.
Numerous schemes for vertical take-off and landing aircraft have been devised in an attempt to increase the horizontal speed capability. One such scheme is to have the aircraft take off in a vertical attitude similar to the Space Shuttle, and then rotate to a horizontal attitude for high speed flight. Another design is to allow the aircraft to take off and land in a horizontal attitude by providing separate engines for vertical and horizontal thrust. Take-off and landing in the horizontal attitude has also been obtained using the same engine for vertical and horizontal flight by vectoring the hot exhaust gases; i.e. either rotating the engine or redirecting the engine thrust. Several examples of existing designs for high speed vertical take-off and land (HSVTOL) aircraft as described, are the Vought TF-120, McDonnell Douglass 279-3 and General Dynamics E-7. In each case, the lift for vertical flight is obtained exclusively from the reaction force of the vectored exhaust gases.
Thus, although there are presently a relatively large number of HSVTOL designs, the prototype of these aircraft have not fully overcome the range, payload and speed shortcomings of the conventional helicopters. Furthermore, these HSVTOL or rotorcraft aircraft are not without their own inherent problems. One problem is that the thrust required for vertical take-off is more than twice the thrust needed for a conventional aircraft and, thus, the engines required are substantially twice as heavy with high fuel consumption, and are expensive to purchase and maintain. Some designs have proposed additional thrust while minimizing expense by utilizing afterburners. However, afterburners create a very hot exhaust which can shorten engine life and harm landing pad surfaces. Additionally, the heat from the exhaust is sometimes reflected upward and is sucked back into the engine causing a loss of power.
Another problem with current HSVTOL designs is the lack of efficient attitude control of the aircraft during both vertical and horizontal flight. The most widely used method to control the attitude presently is a pure reaction control system wherein the exhaust nozzle of the jets is simply moved. This redirects the hot exhaust gas in the manner necessary to pitch and/or roll the aircraft. Usually, this control system is coupled with a separate system of small, compressed air control jets. Because of the lack of stability of these prior aircraft, both are usually required. This increases the cost of the aircraft and is generally inefficient.
In order to attain vertical flight with current HSVTOL aircraft utilizing the reaction jets as described, it is necessary to have the jet engines located as close as possible to the center of gravity. This design requirement greatly increases the control problems and the drag on the aircraft during horizontal flight. Finally, during take-offs and landing, the concentrated vertical stream of exhaust gases being expelled directly from the jet engines causes loose objects on the ground to kick up resulting in damage to the aircraft, commonly referred to as foreign object damage (FOD).